i am of a firm opinion that while Free Group may work as a filter to your paid group / back end mastermind, the biggest mistake one can do is to get traffic without qualifying inside the community. If that is done and they don't have a focused goal, they very soon will feel demotivated and exit the group as you don't want random but only qualified people who want to join a group with that niche.

The same principle applies on a Youtube channel - you can't post random stuff but content for a particular niche which is specific and fit that particular audience avatar